Originally posted by WC
Dunno how much into ICE you are Adz, but there's a lot worse consequences than that.
An underpowered amp (as in "too little voltage in") will pump out jagged signal spikes... this is heard as Distortion & clipping. Distortion is VERY BAD for your speakers!!! Doesn't matter that power rating they are, even if they're in excess of what the amp can pump, distortion will damage your voicecoil and cones.
Imho, most of the "DOOF DOOF" cars have owners with obviously crappy hearing and shot speakers. Their woofers work though!! 
Putting a large capacitor cures most of these underruns... however one large cap eg 1F or 2F (yeah, one Farad) might not have a fast enough response time.
Your sound would become "duOOF duOOF"... 
To cure this we use multiples of smaller caps in parallel... which have a faster response each. Make an array... and they don't even have to be all same size. In fact, different sizes in parallel work better too.
You now have "dUf dUf"... yeah, can't help you on your choice of music there, but you'll notice its a lot 'tighter' and 'better controlled'. It does not necessarily have to be any louder, but you'll start noticing some extra detail in your music. (assuming ears aren't shot already) 
There is no such thing as "too many caps"... I know of systems that can continue running for 5-10s purely on their caps after their main power source has been disconnected. These give good sound, and the last thing you'll think to play on this is a recurring drum beat. 
IMHO most DOOF DOOF cars are crap full stop... never mind the listener... and this comes from aguy who seriously played around in SPL competitions for a couple of years
where are you from WC? your use of the ICE term leads me to think maybe the U.K... the only place where that term has ever been widely used
in My car audio experience 1 farad caps are pretty much "normal" practice now and considered the minimum for a serious system, with most manufacturers such as Stinger etc offering 1.5 farad as well
I've never had ANY experience with lag in response time with large caps... all quality caps start discharging within 1000ths of a second after the power supply is removed... otherwise their purpose in a car audio install is pointless... caps are meant to provide the instant power required by the amplifier to reproduce transient peaks in the music (usually bass related but not always) so unless their response was instant they would be a pointless addition